win32编程 -- 滚轮实现放大或缩小图片

#include <windows.h>
#include "resource.h"
HINSTANCE g_hInstance = 0;//接收当前程序实例句柄
HANDLE g_输出句柄 = 0;//接收标准输出句柄
int g_x = 128;
int g_y = 128;
void 绘图(HWND hWnd)
{
       PAINTSTRUCT p = { 0 };
       HDC hdc = BeginPaint(hWnd, &p);
       HBITMAP hBmp = LoadBitmap(g_hInstance, (wchar_t*)IDB_BITMAP1);
       //到内存dc
       HDC hMDc = CreateCompatibleDC(hdc);
       HGDIOBJ hOBp=SelectObject(hMDc, hBmp);
       StretchBlt(hdc, 0, 0, g_x, g_y, hMDc, 0, 0, 112, 88, SRCCOPY);
     
       //把位图取出来
       SelectObject(hMDc, hOBp);
       DeleteObject(hBmp);
       DeleteDC(hMDc);
         
       EndPaint(hWnd, &p);
}
void 滑轮滚动(HWND hWnd,WPARAM wParam)
{
       short nOf = HIWORD(wParam);
       g_y += nOf / 120;
       g_x += nOf / 120;
       InvalidateRect(hWnd,NULL,TRUE);
}
//2、窗口处理函数
LRESULT CALLBACK WndProc(HWND hWnd, UINT msgID,       
       WPARAM wParam, LPARAM lParam){       
//7、处理消息       
switch (msgID)       
{       
case WM_MOUSEWHEEL:
       滑轮滚动(hWnd,wParam);
              break;
case WM_PAINT:
       绘图(hWnd);
       break;
case WM_DESTROY:              
       PostQuitMessage(0);//销毁窗口              
       break;       
}       
return DefWindowProc(hWnd, msgID, wParam, lParam);
}
//3、注册函数，第一个参数，窗口类名称，第二个参数，指向窗口处理函数的函数指针
void Register(LPCWSTR lpClassName, WNDPROC winProc){       
       WNDCLASSEX wc = { 0 };       
       wc.cbSize = sizeof(wc);//结构体大小      
       wc.cbClsExtra = 0;//窗口类的申请缓存区，0表示不开启缓存       
       wc.cbWndExtra = 0;//窗口的申请缓存区，0表示不开启缓存       
       wc.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);//背景颜色，一般白色       
       wc.hCursor = NULL;//设置光标。null表示默认       
       wc.hIcon = NULL;//默认左上角的图标       
       wc.hInstance = g_hInstance;//第一个参数实例句柄,可以找到进程在那块内存       
       wc.lpfnWndProc = winProc; //lp 一般都是指针,处理函数名或指针       
       wc.lpszClassName = lpClassName;//窗口类名称，比如公司名字       
       wc.lpszMenuName = NULL;//没有菜单用null       
       wc.style = CS_HREDRAW | CS_VREDRAW;//窗口变化，会重绘，窗口类的一般风格       
       RegisterClassEx(&wc);
}
//4、创建窗口,(窗口类名称，窗口标题栏名称)
HWND CreateMain(LPCWSTR lpClassName, LPCWSTR lpWindowName){
       HWND hWnd = CreateWindowExW(0, lpClassName, lpWindowName,  
              WS_OVERLAPPEDWINDOW, 100, 100, 500, 600, NULL, NULL, g_hInstance,  NULL);       
       return hWnd;
}
//5、显示窗口（窗口句柄）
void Display(HWND hWnd){       
       ShowWindow(hWnd, SW_SHOW);//句柄，显示方式       
       UpdateWindow(hWnd);//调用一次刷新窗口
}
//6、消息循环
void Message(){       
       MSG nMsg = { 0 };       
       while (GetMessage(&nMsg, nullptr, 0, 0))       
       {              
              TranslateMessage(&nMsg);              
              DispatchMessage(&nMsg);       
       }
}
//1、入口函数
int CALLBACK WinMain(HINSTANCE hInstance, HINSTANCE hPrevIns, LPSTR lpCmdLine, int  nCmdShow){       
       AllocConsole();//显示dos窗口       
       g_输出句柄 = GetStdHandle(STD_OUTPUT_HANDLE);       
       g_hInstance = hInstance;       
       Register(L"主", WndProc);    
HWND hWnd = CreateMain(L"主", L"主窗口");       
Display(hWnd);       
Message();       
return 0;
}